WIZnet Developer Forum

Problem with Xtal Pins

Hi, I’ve designed a board with TWO W5300 on it,
I used a 25MHz crystal oscillator for each.(
CRYSTAL 25.0MHZ 18PF 20ppm 100 ohm, SMD , MANF PN:ABLS-25.000MHZ-B2F-T)

when I started the hardware test I had no Clock on Xtal Pins, I tried changing Xtal Capacitors by values of 13PF,18PF, 22PF, 33PF, 46PF and 56PF
Now one of them oscillates with 46PF capacitor installed but the other has no oscillation.
I tried changing that Xtal with NTK 25MHz Xtal but also have Problem with it,
Please help me to rectify this problem.

It seems like load-capacitance matching problem.
Load capacitance matching is affected by versatile factors. (pcb routing status, copper thickness(oz)……)
If 18Pf of CL value, theoretically, I recommend 39pF external capacitors. Or, 1.8V level oscillator can be used.

Thanks for reply,

PCB is designed on 50 Ohm tracks like below:
Track width= 4.5 mil,
copper thickness: 3 mil
dielectric constant: 4.3

is 50 ohm impedance matching OK for Xtal Pins?

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